Original entry on oeis.org
2, 23, 2357, 2357137939171, 2357137939171373, 23571379391713739, 2357137939171373917139397137, 2357137939171373917139397137937179, 235713793917137391713939713793717991737391137913793911739171337137177939739397199113939713, 2357137939171373917139397137937179917373911379137939117391713371371779397393971991139397137971939131
Offset: 1
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a[1]=2; a[n_]:=10a[n-1]+Mod[Prime[n], 10];Select[Array[a,100],PrimeQ] (* James C. McMahon, Aug 16 2025 *)
A276481
Numbers k such that b(k) is prime, where b(1) = prime(1) = 2, b(n) = 10*b(n-1) + (prime(n) mod 10).
Original entry on oeis.org
1, 2, 4, 13, 16, 17, 28, 34, 90, 100, 132, 331, 534, 7923, 10157, 40197
Offset: 1
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Res:= NULL: p:= 0: b:= 0:
for n from 1 to 600 do
p:= nextprime(p);
b:= 10*b + (p mod 10);
if isprime(b) then Res:= Res, n fi
od:
Res; # Robert Israel, Sep 05 2016
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b[1] = Prime@ 1; b[n_] := b[n] = 10 b[n - 1] + Mod[Prime@ n, 10]; Select[Range[10^3], PrimeQ@ b[#] &] (* Michael De Vlieger, Sep 06 2016 *)
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b(n) = if (n==1, 2, 10*b(n-1) + (prime(n) % 10));
isok(n) = isprime(b(n)); \\ Michel Marcus, Sep 05 2016
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list(lim)=my(v=List(),s,n); forprime(p=2,, if(n++>lim, return(Vec(v))); if(ispseudoprime(s=10*s+p%10), listput(v, n))) \\ Charles R Greathouse IV, Sep 05 2016
Showing 1-2 of 2 results.
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